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The gun was designed in 1910, and it was probably based on the US 12"/50 (30.5 cm) Mark 7 naval gun with a breech weight added. The guns were manufactured at the Bethlehem Steel Corporation.[1] The ships in the class had twelve 305 mm guns each, mounted in six twin (2-gun) turrets, with two turrets forward, two aft, and one on each side.

The gun weighed 66 tons including the breech and was capable of an average rate of fire of 2–3 rounds a minute. It could throw an 870 lb. (394.6 kg) Mark 15 armor piercing shell 24,000 yards (21,950 meters) at an elevation of 14.7°, while the "barrel life" of the guns was 200 shots.

The previous 12" gun, manufactured for the U.S. Navy, was the Mark 7 version, which had been designed and installed in the 1912 era Wyoming-class battleships.[1]